Room-temperature phosphorescent materials that emit light in the visible (red, green, and blue; from 400 to 700 nm) have been a major focus of research and development during the past decades, due to their applications in organic light-emitting diodes (OLEDs), light-emitting electrochemical cells, photovoltaic cells, chemical sensors, and bio-imaging. In recent years, near-infrared (NIR) phosphorescence beyond the visible region (700–2500 nm) has emerged as a new, promising, and challenging research field with potential applications toward NIR OLEDs, telecommunications, night vision-readable displays. Moreover, NIR phosphorescence holds promise for in vivo imaging, because cells and tissues exhibit little absorption and auto-fluorescence in this spectral region. This review describes the overall progress made in the past ten years on NIR phosphorescent transition-metal complexes including Cu(I), Cu(II), Cr(III), Re(I), Re(III), Ru(II), Os(II), Ir(III), Pt(II), Pd(II), Au(I), and Au(III) complexes, with a primary focus on material design complemented with a selection of optical, electronic, sensory, and biologic applications. A critical comparison of various NIR phosphorescent materials reported in the literature and a blueprint for future development in this field are also provided.

Near-infrared phosphorescence: materials and applications

Although organic multilevel resistance memories have attracted much attention for potential realization of the exponentially-increasing density of data storage, the ambiguous structure–property relationship and the unclear switching mechanism impeded further development of multilevel resistance memory devices Therefore, it is very urgent to ingeniously design multilevel memory materials with a certain switching mechanism In this contribution, we have employed a multi-redox (multiple barriers) polyoxometalate-based inorganic–organic hybrid polymer (whose effective carriers are electrically controllable) to realize a ternary resistance switching memory (multilevel memories) We do believe that the as-designed inorganic–organic polymer can integrate the multi-redox states of the POM and the processability of flexible polymers together The as-fabricated multilevel memory devices exhibit rewriteable switching properties among three redox states by applying different RESET voltages, good endurance with distinct operation windows, and long retention Our results could provide a new strategy to design controllable multilevel resistance memories with excellent performance

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Inorganic–organic hybrid polymer with multiple redox for high-density data storage

At the occasion of the fiftieth birthday of the introduction of the term 'metal atom cluster' by F. A. Cotton in inorganic chemistry, it is the good time to make a review on the advances in the engineering of molecular assemblies and nanomaterials based on octahedral Re6 metal atom clusters. The latter exhibit unique intrinsic structural and physicochemical properties (orthogonal disposition of metallic sites that can be selectively functionalized, photoluminescence, redox, generation of singlet oxygen) that make them relevant building blocks for the structuration at the nanometric scale and functionalization of hybrid organic-inorganic materials and supramolecular frameworks. After synthesis by solid state chemistry techniques at high temperature, inorganic precursors built up on face-capped [(Re6Yi8)Ya6] cluster units (Y = chalcogen and/or halogen) can be functionalized via solution chemistry techniques or organic melts to form [(Re6Yi8)La6] (L = CN, OH, various organic ligands...). This work reports advances in the synthesis of [(Re6Yi8)Ya6] and [(Re6Yi8)La6] cluster units as well as on their use in the elaboration of supramolecular frameworks, nanoparticles, hybrid nanomaterials (co-polymers and liquid crystals) and active molecular junctions.

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Advances in the Engineering of Near Infrared Emitting Liquid Crystals and Copolymers, Extended Porous Frameworks, Theranostic Tools and Molecular Junctions Using Tailored Re6 Cluster Building Blocks

Clusters are ensembles of bound atoms intermediate in size between a molecule and a bulk solid. Some of these clusters form stable units with atomically precise structures that give rise to collective behaviours that mimic those of traditional atoms, essentially functioning as ‘superatoms’. Such superatoms are exciting, nanoscale building blocks for materials design. Sustained synthetic and theoretical efforts over the past 40 years have created a vast library of chemically tuneable superatoms that display unique physical and chemical properties. The use of superatoms as building blocks for materials offers opportunities to design materials with tailored functionalities; however, this potential has only begun to be realized in the past few years. The assembly of superatomic crystals presents numerous challenges, including the design of suitable building blocks, control of the self-assembly process, promotion of strong inter-superatom coupling and understanding the resulting collective properties. In this Review, we assess recent advances in meeting these challenges by focusing on metal chalcogenide and carbon-based clusters (for example, fullerenes) as superatomic building blocks. Molecular clusters can be used as tuneable, superatomic building blocks to create new functional materials. This Review outlines the synthesis and assembly of superatoms into superatomic crystals and the resulting collective material properties.

Superatoms in materials science

The paper reports on the high photocatalytic activity of [Mo6Br8(N3)6]2− cluster units for the degradation of rhodamine B under UV, visible or sun light irradiation. Water soluble Na2[Mo6Br8(N3)6] inorganic compound built up from [Mo6Br8(N3)6]2− anionic cluster units associated with Na+ counter cations investigated in this work is prepared in high yield by the interaction of Mo6Br12 with sodium azide in methanol. The high photocatalytic performance of the molybdenum cluster is demonstrated under real solar light excitation, suggesting that the photocatalyst could be used in broad daylight hours. Furthermore, the cluster is still highly active after ten successive cycling runs under UV or visible light irradiation without any apparent loss of its efficiency.

Fast photocatalytic degradation of rhodamine B over [Mo6Br8(N3)6]2− cluster units under sun light irradiation

The embedding of functional inorganic entities into polymer matrices has become an intense field of investigation in which the main challenges are to keep the added value of the inorganic entities while preventing their self-aggregation within the organic matrix. We present a simple way to obtain a homogeneous highly red-NIR luminescent hybrid copolymer that contains covalently bonded nanometric-sized {Re(6)} octahedral clusters. The [Re(6)Se(i)(8)(OH)(a)(6)](4-) cluster complexes are primarily functionalized in two steps with tert-butylpyridine (TBP) and methacrylic acid (MAC) to give neutral [Re(6)Se(8)(TBP)(4)(MAC)(2)] building blocks that are copolymerized with methyl methacrylate (MMA) either in solution or in bulk in the presence of azobisisobutyronitrile as an initiator. Several samples containing 0, 0.025, 0.05, and 0.1 wt % of functionalized {Re(6)} clusters were prepared. As the {Re(6)} cluster/MMA ratio is very low, the obtained copolymers keep the entire processability of pure poly(methyl methacrylate) (PMMA), as demonstrated by differential scanning calorimetry and thermogravimetric analysis. Voltammetric and luminescence studies also indicate that the intrinsic properties of the clusters are preserved within the polymer matrix. All the samples show a bright (emission quantum yield=0.07), broad, and structureless emission band, which extends from lambda=600 nm to more than lambda=950 nm, with the maximum wavelength centered around lambda(em)=710 nm either in solution or in the solid state. Moreover, the high stability of the incorporated inorganic phosphors prevents the material from photobleaching, and thus the luminescence properties are kept entirely even after nine months of ageing.

Yann Le Gal

Papers

Red‐NIR Luminescent Hybrid Poly(methyl methacrylate) Containing Covalently Linked Octahedral Rhenium Metallic Clusters